<!DOCTYPE html>
<html lang="zh-CN">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .fu {
      /* 父类缩小到,所有的子类内部紧挨边框,不在缩小
      子类默认高度是父类的高
      */
      display: flex;
      background-color: aqua;
      height: 500px;
      width: 600px;
    }
/* 在子类里边添加flex 将剩余空间,按照分数均分, 均分宽>设置的宽 */
    .son {
      border: 1px solid #ccc;
      width: 100px;
      height: 100px;
      flex: 1;
    }

    .son:nth-child(2) {
      flex: 2
    }

    span {
      width: 100px;
      border: 1px solid #ccc;
      height: 100px;
    }
  </style>
</head>

<body>
  <div class="fu">
    <div class="son">div1</div>
    <div class="son">div2</div>
    <div class="son">div3</div>
    <span>我是sapn</span>
  </div>

  <!-- <p>我是p标签</p> -->
</body>

</html>